In general, contour lines for determining a model of a three-dimensional (3D) object are calculated using 3D information. A contour line determines one reference face, and uses the neighboring information of the face. The scalar products between normal information of the face and normal information of neighboring faces are calculated, and neighboring faces, having a negative scalar product value, are determined. Edges that are boundaries between determined neighboring faces and the reference face are edges that are a contour.
The above-described method is a well-known silhouette determination algorithm. Edges calculated as described above are stored in a data structure. A silhouette includes edges that are a boundary between a front face and a back face.
Meanwhile, the prior art related to a method of realistically representing a line style will be described below.
The prior art technology for representing a line style includes “Stylized Haloed Outlines on the GPU,” authored by “Jörn Loviscach” and published in “SIGGRAPH 2004 Poster.” According to the prior art, outlines are extracted from a 3D model, and transparency is adjusted by adjusting an alpha value by a value corresponding to a specific thickness in the areas around the outlines in order to make the break between a visible line and an invisible line natural. Curved lines are formed by slightly modifying silhouette curves in order to realize natural representation which appears to have been drawn by a human hand. In order to realize the effect in which a plurality of lines appears to have been drawn in an overlay fashion, color values are modified at texture coordinates using Perlin noise textures. The prior art technology proposes a method that has a high speed due to the use of a Graphics Processing Unit (GPU)-based rendering technique, and can create images that appear to have been drawn by a human hand.
Korean Laid-open Patent Publication No. 2007-0019953 entitled “Apparatus and Method for Representing Relative Location of Moving Object” discloses a method of calculating the relative motion of an object using the intensity of radio waves or radio wave propagation time.
U.S. Pat. No. 7,061,501, entitled “Rendering a Pencil-Sketch Image,” discloses a method of projecting 3D data onto a two-dimensional surface, mapping a pencil-sketch texture, and finally creating a pencil-sketch image.
As described above, a lot of research into the representation of the effect of appearing to have been drawn by a human hand at the time of representing a line style in the field of non-photo realistic rendering has been conducted.